In general, the invention relates to novel methods for silencing genes. Desirably, these methods specifically inhibit the expression of one or more target genes in a cell or animal (e.g., a mammal such as a human) without inducing toxicity.
Double stranded RNA (dsRNA) has been shown to induce gene silencing in a number of different organisms. Gene silencing can occur through various mechanisms, one of which is post-transcriptional gene silencing (PTGS). In post-transcriptional gene silencing, transcription of the target locus is not affected, but the RNA half-life is decreased. Transcriptional gene silencing (TGS) is another mechanism by which gene expression can be regulated. In TGS, transcription of a gene is inhibited. Exogenous dsRNA has been shown to act as a potent inducer of PTGS in nematodes, trypanosomes, and insects. Double stranded RNA is also an inducer of TGS. Some current methods for using dsRNA in vertebrate cells to silence genes result in undesirable non-specific cytotoxicity or cell death due to the interferon response that is induced by dsRNA in vertebrate cells. Some methods also result in non-specific or inefficient silencing.
Thus, improved methods are needed for specifically silencing target genes without inducing toxicity or cell death. Desirably, these methods may be used to inhibit gene expression in in vitro samples, cell culture, and intact animals (e.g., vertebrates such as mammals).